302 PROCEEDINGS OF THE NATIONAL MUSEUM vol.83 



Inferior dentition. — The lower incisors are large and broad, with 

 the enamel on the labial surface thicker than that on the lingual 

 surface and generally grooved or slightly irregular. The cup in the 

 first two incisors is well toward the lingual surface and is less deeply 

 impressed than in the upper incisors, as it is more rapidly reduced or 

 obliterated, particularly in Ij. In unworn Ij and I2 the inner wall 

 of the tooth is appreciably lower than the outer and generally uneven 

 or cuspate. I3 is broadly open on the lingual side and in most cases 

 does not exhibit a lingual stylar cusp, nor does the enamel form a cup, 

 although in a few instances a small cup is present. 



The lower canine, lying a short distance posterior to the third 

 incisor, is very similar in the males to that in the upper jaw, though 

 perhaps a Uttle smaller. In the females the tooth is small, occasionally 

 absent, but generally more erect than in E. grevyi. 



Pi is usually present in young specimens; associated with the milk 

 dentition, to which series it may weU belong. It is a small simple 

 conical cusp, not unlike that seen in young specimens of E. grevyi. 

 Unlike P' this tooth is apparently lost with the eruption of the per- 

 manent premolars. 



The lower cheek teeth (fig. 22) are large, robust, and heavily 

 cemented, with little or no lateral curvature. The greatest width is 

 generally across the third premolar or second tooth in the series. 

 The pattern of the teeth though variable is rather simple and with 

 few or no plications on the major reentrants on the lingual side of the 

 teeth, except in early stages of wear. The two internal enamel 

 reentrants of the premolars in early wear may show an irregular 

 plicate condition, more noticeable in the posterior fold in which a 

 slight pUcation opposite the ectostyUd persists in some dentitions 

 to advanced wear. These Ungual loops are as extensive as in recent 

 Equus dentitions but are generally less compressed transversely. 



The parastjdid is simple and of variable length and commonly shows 

 a single flexure about midway along the posterior wall, except in P2 

 where the development characteristic of tliis tooth is seen. In a 

 few instances in P3, in dentitions where the parastyhd is shortest, a 

 slight style is seen extending outward from the antero-external angle 

 of the tooth. In one case, no. 12533, this portion of the tooth appears 

 as if the parastylid were reversed and directed externally. 



The metaconid-metastyhd columns are usually simple and rounded, 

 with the metastylid possibly somewhat less angular than is usual 

 in the Equus material observed. The groove between the columns 

 is generally acute but on the average much shallower or less deeply 

 impressed than in E. grevyi or E. caballus. In E. caballus this groove 

 is usually more widely open. 



